1. Example 4.1 Stoichiometry
In photosynthesis, plants convert carbon dioxide and water into glucose (C6H12O6) according to the reaction:
Suppose you determine that a particular plant consumes 37.8g of CO2 in one week. Assuming that there is more than enough water present to react with all of the CO2, what mass of glucose (in grams) can the plant synthesize from the CO2? Answer: 25.8 g C6H12O5

2. Example 4.1 Stoichiometry
For Practice 4.1
Magnesium hydroxide, the active ingredient in milk of magnesia, neutralizes stomach acid, primarily HCl, according to the reaction:
What mass of HCl, in grams, is neutralized by a dose of milk of magnesia containing 3.26 g Mg(OH)2?
Mg(OH)2 = amu ; HCl = amu Answer: 4.08 g HCl

3. Example 4.2 Stoichiometry
Sulfuric acid (H2SO4) is a component of acid rain that forms when SO2, a pollutant, reacts with oxygen and water according to the simplified reaction:
The generation of the electricity used by a medium-sized home produces about 25 kg of SO2 per year. Assuming that there is more than enough O2 and H2O, what mass of H2SO4, in kg, can form from this much SO2?
1 kg = g 2 mol SO2 : 2 mol H2SO4
molar mass SO2 = g/mol molar mass H2SO4 = g/mol
Answer: 38 Kg
For Practice 4.2
Another component of acid rain is nitric acid, which forms when NO2, also a pollutant, reacts with oxygen and water according to the simplified equation:
The generation of the electricity used by a medium-sized home produces about 16 kg of NO2 per year. Assuming that there is adequate O2 and H2O, what mass of HNO3, in kg, can form from this amount of NO2 pollutant?
NO2 = = ; HNO3 =
Answer: 22 Kg

4. Example 4.3 Limiting Reactant and Theoretical Yield
Ammonia, NH3, can be synthesized by the reaction:
Starting with 86.3 g NO and 25.6 g H2, find the theoretical yield of ammonia in grams.
Relationships Used
molar mass NO = g/mol
molar mass H2 = 2.02 g/mol
2 mol NO : 2 mol NH3 (from chemical equation)
5 mol H2 : 2 mol NH3 (from chemical equation)
molar mass NH3 = g/mol
For Practice 4.3
Ammonia can also be synthesized by the reaction:
What is the theoretical yield of ammonia, in kg, that we can synthesize from 5.22 kg of H2 and 31.5 kg of N2?

5. Example 4.4 Limiting Reactant and Theoretical Yield
We can obtain titanium metal from its oxide according to the following balanced equation:
When 28.6 kg of C reacts with 88.2 kg of TiO2, 42.8 kg of Ti is produced. Find the limiting reactant, theoretical yield (in kg), and percent yield.
Relationships Used
1000 g = 1 kg
1 mol TiO2 : 1 mol Ti
molar mass of C = g/ mol
2 mol C : 1 mol Ti
molar mass of TiO2 = g/ mol
molar mass of Ti = g/mol
Answer: 52.9 Kg Ti

6. Example 4.4 Limiting Reactant and Theoretical Yield
For Practice 4.4
Mining companies use this reaction to obtain iron from iron ore:
The reaction of 167 g Fe2O3 with 85.8 g CO produces 72.3 g Fe. Determine the limiting reactant, theoretical yield, and percent yield.
Fe2O3 = * *3 =
Answer = 114 g Fe and Yield = 63.4 %

7. Example 4.5 Calculating Solution Concentration
If you dissolve 25.5 g KBr in enough water to make 1.75 L of solution, what is the molarity of the solution?
Sort
You are given the mass of KBr and the volume of a solution and asked to find its molarity.
Given: 25.5 g KBr, 1.75 L of solution
Find: molarity (M)
Answer: M

8. Example 4.5 Calculating Solution Concentration
Continued
For Practice 4.5
Calculate the molarity of a solution made by adding 45.4 g of NaNO3 to a flask and dissolving it with water to create a total volume of 2.50 L.
Mol. Wt. of NaNO3 = *3 = 85 g/mol
Answer: M
For More Practice 4.5
What mass of KBr (in grams) do you need to make mL of a 1.50 M KBr solution?
Mol. Wt. KBr = = 120 g/mol
Answer: 45.0 g KBr

9. Example 4.6 Using Molarity in Calculations
How many liters of a M NaOH solution contain mol of NaOH?
Given: M NaOH solution, mol NaOH
Find: volume of NaOH solution (in L)
For Practice 4.6
How many grams of sucrose (C12H22O11) are in 1.55 L of M sucrose solution?
C12H22O11 = 12* * *16.00 =
402 g
For More Practice 4.6
How many mL of a M KCl solution contain 2.55 g KCl?
KCl = =
Answer = 221 mL

10. Example 4.7 Solution Dilution
To what volume should you dilute L of a 15.0 M NaOH solution to obtain a 3.00 M NaOH solution?
Sort
You are given the initial volume, initial concentration, and final concentration of a solution, and you need to determine the final volume.
Given: V1 = L
M1 = 15.0 M
M2 = 3.00 M
Find: V2
For Practice 4.7
To what volume (in mL) should you dilute mL of a 5.00 M CaC2 solution to obtain a M CaC2 solution?
For More Practice 4.7
What volume of a 6.00 M NaNO3 solution should you use to make L of a 1.20 M NaNO3 solution?

11. Example 4.8 Solution Stoichiometry
What volume (in L) of M KCl solution will completely react with L of a M Pb(NO3)2 solution according to the following balanced chemical equation?
Sort
You are given the volume and concentration of a Pb(NO3)2 solution. You are asked to find the volume of KCl solution (of a given concentration) required to react with it.
Given: L of Pb(NO3)2 solution, M
Pb(NO3)2 solution, M KCl solution
Find: volume KCl solution (in L)
Strategize
The conceptual plan has the form: volume A → amount A (in moles) → amount B (in moles) → volume B. Use the molar concentrations of the KCl and Pb(NO3)2 solutions as conversion factors between the number of moles of reactants in these solutions and their volumes. Use the stoichiometric coefficients from the balanced equation to convert between number of moles of Pb(NO3)2 and number of moles of KCl.

12. Example 4.8 Solution Stoichiometry
Continued
Conceptual Plan
Relationships Used

13. Example 4.8 Solution Stoichiometry
Continued
For Practice 4.8
What volume (in mL) of a M HNO3 solution will completely react with 35.7 mL of a M Na2CO3 solution according to the following balanced chemical equation? Answer: 51.4 mL HNO3
For More Practice 4.8
In the previous reaction, what mass (in grams) of carbon dioxide forms? Answer: g CO2

14. Example 4.9 Predicting whether an Ionic Compound Is Soluble
Predict whether each compound is soluble or insoluble.
a. PbCl2 b. CuCl2 c. Ca(NO3) d. BaSO4
Solution
a. Insoluble. Compounds containing Cl− are normally soluble, but Pb2+ is an exception.
b. Soluble. Compounds containing Cl− are normally soluble and Cu2+ is not an exception.
c. Soluble. Compounds containing NO3− are always soluble.
d. Insoluble. Compounds containing SO42− are normally soluble, but Ba2+ is an exception.
Strategize
Predict whether each compound is soluble or insoluble.
a. NiS b. Mg3(PO4) c. Li2CO d. NH4Cl

15. Example 4.10 Writing Equations for Precipitation Reactions
Write an equation for the precipitation reaction that occurs (if any) when solutions of potassium carbonate and nickel(II) chloride are mixed.
Procedure For…
Writing Equations for Precipitation Reactions
Step 1 Write the formulas of the two compounds being mixed as reactants in a chemical equation.
Step 2 Below the equation, write the formulas of the products that could form from the reactants. Obtain these by combining the cation from each reactant with the anion from the other. Make sure to write correct formulas for these ionic compounds using the procedure demonstrated in Section 3.5.
Step 3 Refer to the solubility rules to determine whether any of the possible products are insoluble.
KCl is soluble. (Compounds containing Cl− are usually soluble and K+ is not an exception.)
NiCO3 is insoluble. (Compounds containing CO32− are usually insoluble and Ni2+ is not an exception.)

16. Example 4.10 Writing Equations for Precipitation Reactions
Continued
Step 4 If all of the possible products are soluble, there will be no precipitate. Write “NO REACTION” after the arrow.
Since this example has an insoluble product, we proceed to the next step.
Step 5 If any of the possible products are insoluble, write their formulas as the products of the reaction, using (s) to indicate solid. Write any soluble products with (aq) to indicate aqueous.
Step 6 Balance the equation. Remember to adjust only coefficients, not subscripts.
For Practice 4.10
Write an equation for the precipitation reaction that occurs (if any) when solutions of ammonium chloride and iron(III) nitrate are mixed.

17. Example 4.11 Writing Equations for Precipitation Reactions
Write an equation for the precipitation reaction that occurs (if any) when solutions of sodium nitrate and lithium sulfate are mixed.
Procedure For…
Writing Equations for Precipitation Reactions
Step 1 Write the formulas of the two compounds being mixed as reactants in a chemical equation.
Step 2 Below the equation, write the formulas of the products that could form from the reactants. Obtain these by combining the cation from each reactant with the anion from the other. Make sure to write correct formulas for these ionic compounds using the procedure demonstrated in Section 3.5.
Step 3 Refer to the solubility rules to determine whether any of the possible products are insoluble.
LiNO3 is soluble. (Compounds containing NO3− are soluble and Li+ is not an exception.)
Na2SO4 is soluble. (Compounds containing SO42− are generally soluble and Na+ is not an exception.)

18. Example 4.11 Writing Equations for Precipitation Reactions
Continued
Step 4 If all of the possible products are soluble, there will be no precipitate. Write “NO REACTION” after the arrow.
Since this example has no insoluble product, there is no reaction.
Step 5 If any of the possible products are insoluble, write their formulas as the products of the reaction, using (s) to indicate solid. Write any soluble products with (aq) to indicate aqueous.
Step 6 Balance the equation. Remember to adjust only coefficients, not subscripts.
For Practice 4.11
Write an equation for the precipitation reaction that occurs (if any) when solutions of sodium hydroxide and copper(II) bromide are mixed.

19. Example 4.12 Writing Complete Ionic and Net Ionic Equations
Write complete ionic and net ionic equations for each reaction. a. b.
Solution
a. Write the complete ionic equation by separating aqueous ionic compounds into their constituent ions. The Sr3(PO4)2(s), precipitating as a solid, remains as one unit.
Write the net ionic equation by eliminating the spectator ions, those that do not change from one side of the
reaction to the other.
Complete ionic equation:
Net ionic equation:

20. Example 4.12 Writing Complete Ionic and Net Ionic Equations
Continued
b. Write the complete ionic equation by separating aqueous ionic compounds into their constituent ions. Do not separate HC2H3O2(aq) because it is a weak electrolyte.
Write the net ionic equation by eliminating the spectator ions.
Complete ionic equation:
Net ionic equation:
For Practice 4.12
Consider the following reaction occurring in aqueous solution:
Write the complete ionic equation and net ionic equation for this reaction.

21. Example 4.13 Writing Equations for Acid–Base Reactions
Write a molecular and net ionic equation for the reaction between aqueous HI and aqueous Ba(OH)2.
Solution
First identify these substances as an acid and a base. Begin by writing the unbalanced equation in which the acid and the base combine to form water and a salt.
Next, balance the equation; this is the molecular equation.
Write the net ionic equation by removing the spectator ions.
For Practice 4.13
Write a molecular and a net ionic equation for the reaction that occurs between aqueous H2SO4 and aqueous LiOH.

22. Example 4.14 Acid–Base Titration
The titration of a mL sample of an HCl solution of unknown concentration requires mL of a M NaOH solution to reach the equivalence point. What is the concentration of the unknown HCl solution in M?
Sort
You are given the volume and concentration of NaOH solution required to titrate a given volume of HCl solution. You are asked to find the concentration of the HCl solution.
Given: mL of NaOH solution, M NaOH solution, mL of HCl solution
Find: concentration of HCl solution
Strategıze
Since this problem involves an acid–base neutralization reaction between HCl and NaOH, you start by writing the balanced equation, using the techniques covered earlier in this section.
The first part of the conceptual plan has the form volume A → moles A → moles B. The concentration of the NaOH solution is a conversion factor between moles and volume of NaOH. The balanced equation provides the relationship between number of moles of NaOH and number of moles of HCl.
In the second part of the conceptual plan, use the number of moles of HCl (from the first part) and the volume of HCl solution (given) to calculate the molarity of the HCl solution.

23. Example 4.14 Acid–Base Titration
Continued
Conceptual Plan
Relationships Used

24. Example 4.14 Acid–Base Titration
Continued
Solve
In the first part of the solution, determine the number of moles of HCl in the unknown solution.
In the second part of the solution, divide the number of moles of HCl by the volume of the HCl solution in L mL is equivalent to L.
Solution
Check
The units of the answer (M HCl) are correct. The magnitude of the answer (0.125 M) is reasonable because it is similar to the molarity of the NaOH solution, as expected from the reaction stoichiometry (1 mol HCl reacts with 1 mol NaOH) and the similar volumes of NaOH and HCl.

25. Example 4.14 Acid–Base Titration
Continued
For Practice 4.14
The titration of a 20.0 mL sample of an H2SO4 solution of unknown concentration requires mL of a M KOH solution to reach the equivalence point. What is the concentration of the unknown H2SO4 solution?
Answer: 9.03 x10-3 M H2SO4
For More Practice 4.14
What volume (in mL) of M NaOH do we need to titrate mL of M HBr to the equivalence point?

26. Example 4.15 Writing Equations for Gas-Evolution Reactions
Write a molecular equation for the gas-evolution reaction that occurs when you mix aqueous nitric acid and aqueous sodium carbonate.
Begin by writing an unbalanced equation in which the cation of each reactant combines with the anion of the other.
You must then recognize that H2CO3(aq) decomposes into H2O(l) and CO2(g) and write these products into the equation.
Finally, balance the equation.
For Practice 4.15
Write a molecular equation for the gas-evolution reaction that occurs when you mix aqueous hydrobromic acid and aqueous potassium sulfite.
For More Practice 4.15
Write a net ionic equation for the reaction that occurs when you mix hydroiodic acid with calcium sulfide.

27. Example 4.16 Assigning Oxidation States
Assign an oxidation state to each atom in each element, ion, or compound.
a. Cl2 b. Na+ c. KF d. CO2 e. SO42− f. K2O2
Solution
a. Since Cl2 is a free element, the oxidation state of both Cl atoms is 0 (rule 1).
b. Since Na+ is a monoatomic ion, the oxidation state of the Na+ ion is +1 (rule 2).
c. The oxidation state of K is +1 (rule 4). The oxidation state of F is −1 (rule 5). Since this is a neutral compound, the sum of the oxidation states is 0.

28. Example 4.16 Assigning Oxidation States
Continued
d. The oxidation state of oxygen is −2 (rule 5). The oxidation state of carbon must be deduced using rule 3, which says that the sum of the oxidation states of all the atoms must be 0.
e. The oxidation state of oxygen is −2 (rule 5). We would ordinarily expect the oxidation state of S to be − (rule 5). However, if that were the case, the sum of the oxidation states would not equal the charge of the ion Since O is higher on the list than S, it takes priority and we compute the oxidation state of sulfur by setting the sum of all of the oxidation states equal to −2 (the charge of the ion).

29. Example 4.16 Assigning Oxidation States
Continued
f. The oxidation state of potassium is +1 (rule 4). We would ordinarily expect the oxidation state of O to be − (rule 5), but rule 4 takes priority, and we deduce the oxidation state of O by setting the sum of all of the oxidation states equal to 0.
For Practice 4.16
Assign an oxidation state to each atom in each element, ion, or compound.
a. Cr b. Cr c. CCl d. SrBr e. SO f. NO3−

30. Example 4.17 Using Oxidation States to Identify Oxidation and Reduction
Use oxidation states to identify the element that is oxidized and the element that is reduced in the following redox reaction.
Solution
Begin by assigning oxidation states to each atom in the reaction.
Since Mg increased in oxidation state, it was oxidized. Since H decreased in oxidation state, it was reduced.
For Practice 4.17
Use oxidation states to identify the element that is oxidized and the element that is reduced in the following redox reaction.

31. Example 4.17 Using Oxidation States to Identify Oxidation and Reduction
Continued
For More Practice 4.17
Determine whether or not each reaction is a redox reaction. If the reaction is a redox reaction, identify which element is oxidized and which is reduced.

32. Example 4.18 Identifying Redox Reactions, Oxidizing Agents, and Reducing Agents
Determine whether each reaction is an oxidation–reduction reaction. For each oxidation–reduction reaction, identify the oxidizing agent and the reducing agent. a. b. c.
Solution
a. This is a redox reaction because magnesium increases in oxidation number (oxidation) and oxygen decreases in oxidation number (reduction).
b. This is not a redox reaction because none of the atoms undergo a change in oxidation number.

33. Example 4.18 Identifying Redox Reactions, Oxidizing Agents, and Reducing Agents
Continued
c. This is not a redox reaction because none of the atoms undergo a change in oxidation number.
For Practice 4.18
Determine whether or not each reaction is a redox reaction. For all redox reactions, identify the oxidizing agent and the reducing agent. a. b. c. d.

34. Example 4.19 Writing Equations for Combustion Reactions
Assign an oxidation state to each atom in each element, ion, or compound.
Solution
Begin by writing an unbalanced equation showing the reaction of CH3OH with O2 to form CO2 and H2O.
Balance the equation using the guidelines in Section 3.10.
For Practice 4.19
Write a balanced equation for the complete combustion of liquid C2H5SH.